huangyhg

slenderness - in-plane moment
elders,
i have a question regarding how the t/c due to a huge in-plane moment on a tall planar wall is accounted for.
for example if i had a 30' long wall with 20' story heights laterally supporting a 20 story building, what kind of localized compression behavior would be present towards the outer core of the wall? would the high compressive force induce some sort of local buckling? i am not able to visualize it completely, and the only thing i can visualize is a warping of this 20' high wall (akin to a pseudo s shape).
any ideas?
not an easy question to answer in a few words... what i do is analyze the wall as a singly reinforced vertical concrete beam, assuming a triangular stress block. the rub is you have axial load as well as bending, and the solution for the equilibrium condition involves solving a cubic equation. a review of your concrete design college textbook should give you the info you need.
you solve for not only the tension in the steel, but the "extreme fiber compressive stress" in the concrete at the end of the wall. this "stress" is normally expressed in terms of kips-per-foot. you can average this compressive stress over whatever wall segment increments you choose based on judgement, and design each segment of wall as a column.
one further complication is where do you analyze the "column" section, since axial stress varies over the story height... do you analyze at mid-height of each story/unbraced length to get an "average" axial load?... at the top & bottom and "average" that way? do you base the assumed width of column on the shape of the stress blocks top & bottom? since the axial load varies over the height of the "column", do you assume a reduced k-factor for minor axis/out-of-plane slenderness considerations? all of this involves some engineering judgement.
i know this is not a totally thorough explaination, but it's a direction.

__________________
借用达朗贝尔的名言：前进吧，你会得到信心!
[url="http://www.dimcax.com"]几何尺寸与公差标准[/url]